My 12-year old has just asked to participate in another weekly activity thirty minutes away. I try a quick rebuff: “You’re already too busy and it’s too expensive.”

With more than a bit of adolescent attitude, she replies, “You just don’t want to take the time to drive me.”

I look at the clock. It’s past 7:00 PM. We haven’t eaten dinner, and unfinished homework clutters the kitchen table. There is never a perfect moment to get into the real nitty gritty of why and wherefore. Still, sometimes you have to take the time to give your kids an honest answer to their questions.

“Yes, you’re partly right,” I tell her, and her sister too, who has now wandered in. “I don’t especially want to spend more time carting you around. But there is another reason. Every time we get in the car we contribute to climate change. By the end of this century — and you may both still be around — climate change is likely to make conditions for life on earth drastically different from what they are today.”

I pause. It’s gloomy stuff, the state of the environment. Usually I try not to dwell on scientists’ pessimistic planetary forecasts. Nobody, including me, really wants to hear it. Nobody wants to read about it over morning coffee and a doughnut. Nobody wants to tell their kids about it.

I plunge ahead. I tell them that they have just lived through the hottest decade ever recorded. I tell them that recent flooding submerged one fifth of the land surface of Pakistan, washing away 7,000 schools.

I tell them that the Arctic is melting, that hurricanes are getting stronger, droughts are lengthening, and rainfall records are being shattered. Within their lifetimes, sea level could rise by 6 feet, or more, submerging the world’s coastal cities.

The children are quiet. Finally they ask if our house, a few miles inland from the Maine coast, will be okay. This question, in its innocent disregard either for the welfare of others, or for the fact that if the world disintegrates around them it won’t matter if their house is okay, seems to reflect a child’s perspective.

But it’s how us adults think too: Sure, catastrophic drought struck Texas last year and the Midwest this summer. But here in the Northeast global warming so far has mostly meant warmer winters. In other words, our house and family are fine.

Well then, my children ask, shouldn’t we do something about it?

I tell them they are already helping by riding their bikes and walking around town, by delighting in hand-me-downs rather than shopping trips, by eating local spinach rather than asking for processed foods from afar.

Although this cheers them up a bit, they are smart enough to know that a few leaves of spinach are not going to fix a whole lot. By the end of the conversation, they’re in tears.

Like every parent, I want my children to believe their futures are full of hope and promise. Yet at some point they also need to look with clear eyes at the world around them. Without that, where will the motivation come from to make anything better?

Still, our own family’s behavior is riddled with inconsistencies. Save the planet by biking to school, but drive two hours for a ski weekend. Buy local greens at the farmer’s market then wash them down with inexpensive California red wine, trucked from 3,000 miles away.

Humans, however, can live with inconsistency. So I tell my kids what I tell myself. “For today, pick one action to work on. Turn off the lights when you come downstairs. Nudge yourself.” I’m a nudger.

But in my heart of hearts I know that we need world-changers, not nudgers, and I don’t know where to send my children for training.